Changes in the secretion of insulin and its effectiveness were studied following 20% body surface burn in the rat. The injury resulted in a short inhibition of insulin secretion followed by a suggestion of insulin resistance. To study the latter, rats fasted overnight were injected with lg glucose/kg b.w. intravenously at 1 to 7 days post-burn and the average hyperinsulinemic and hyperglycemic responses were expressed as the area under the curve above the initial value. Areas of timed controls represented 100%. The insulin response of burned rats was 101% on day 1, 147% on day 2, reached its peak of 169% on day 3 and decreased to 141% on day 4, 108% on day 5, 115% on day 6 and 128% on day 7. During the same period the areas under the glucose curve did not differ appreciably from controls. Nor was there any clear relationship to fasting serum glucose which was 68 plus or minus 7 (SE) mg/100 ml higher than control on day 1 and returned almost linearly to control level on day 4. Fasting plasma glucagon was 2-fold (p less than 0.01) higher and corticosterone 4.7-fold (p less than 0.01) higher than control on day 1, but both hormones virtually returned to control level on day 3 when the post-glucose hyperinsulinemia of burned rats was maximal. The development of the exaggerated post-glucose hyperinsulinemia was also observed in separate experiment when caloric intake was controlled. CONCLUSION: Burn injury in the rat is followed by a late development of the exaggerated insulin response to glucose. This does not seem to be directly caused by changes in food intake, an abnormal glucose stimulus or presence of glucagon or corticosterone in blood. BIBLIOGRAPHIC REFERENCES: Turinsky, J., L. Loose and W.A. Scovill. Anti-insulin hormones and the development of exaggerated insulin response after burn injury. Proc. of the 9th Annual Meeting of the American Burn Association in Anaheim, CA, p. 51-52, 1977, in press. Scovill, W.A., J. Turinsky, and L. Loose. Effect of temperature on hepatic gluconeogenesis after burns. Proc. of the 9th Annual Meeting of the American Burn Association, Anaheim, CA, p. 53-54, 1977, in press.